1. Field of the Invention
The present invention relates to a portable terminal device and method of operation, and more particularly to a portable terminal device which is driven by batteries.
2. Description of the Related Art
Many types of battery driven portable terminal devices have been developed and used in fields such as finance, traffic, and the like. These portable terminal devices have a central processing unit (CPU), a display device, a keyboard, a memory, and a battery pack. The battery pack provides a predetermined amount of power to each component within the portable terminal device.
Due to the need for lightweight portable terminal device, lightweight battery pack which provide only a few hours of continuous operation on a given charge must be used within them. If the battery power of these battery packs falls below a certain threshold power value, both buffered and processing data can be lost. For this reason, it is advantageous to provide a monitoring system for this portable terminal device power, insuring that no buffered or processed data is lost due to power failures.
A device for preventing unintentional loss of data in a terminal device due to electrical power failure is disclosed in U.S. Pat. No. 4,763,333. This device comprises a main power battery, a continuously powered memory, and a monitor circuit for generating signals during battery power failure.
A ROM is provided which executes stored programs during power failure. These stored programs take over control of the terminal device and store the current state of the CPU in the continuously powered memory.
Note that in this device, a power failure is detected via status signals which are sent from the monitor circuit during a routine and periodic check of the battery. Thus, in this conventional device, the battery power consumption is increased by the system used to check it.